1 Physiological Response to An Auditory Startle Stimulus Under Relaxed and Occupied Conditions University of Wisconsin-Madison Department of Physiology Physiology 435 Lab 601-5: Maddy Eckelaert, Jai Patel, Michelle Cancel, Zach Bennet, Miki Hirano, Ashley Verhasselt May 11 th 2012
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Physiological Response to An Auditory Startle Stimulus Under
Relaxed and Occupied Conditions
University of Wisconsin-Madison Department of Physiology
Physiology 435 Lab 601-5: Maddy Eckelaert, Jai Patel, Michelle Cancel, Zach Bennet,
Miki Hirano, Ashley Verhasselt
May 11th
2012
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Abstract
This study aims to investigate if an individual’s physiological response to a auditory
startle stimulus, preceded by a auditory warning stimulus, depends on whether or not they are in
a relaxed versus occupied condition. Two groups of eight participants were respectively placed
into one of these conditions. Three physiological responses were measured throughout the
duration of the study: heart rate, respiration rate, and skin conductance. During both the relaxed
and occupied conditions, subjects first focused on an object (30s). Then, relaxed condition
participants continued this task while occupied condition participants began work on a word
search (60s). Next, both conditions received a warning stimulus and 10s after introduction, the
startle stimulus was administered. A greater physiological response (increased heart activity,
increased respiratory activity and increased perspiration) was expected in response to the startle
stimulus in a relaxed condition versus an occupied condition. The relaxed and occupied groups
only exhibited a significant difference in max GSR values (p = 0.04). Comparing the post-
warning and post-stimulus conditions, both relaxed (p = 0.01) and occupied groups (p = 0.05)
exhibited a significant difference in GSR values. Comparing positive and negative controls, the
relaxed group exhibited significant values for max heart rate (p = 3.89x10-6
) and max respiration
(p = 0.03) and the occupied group exhibited significant values for (p = 3.89x10-6
) and max
respiration (p = 0.03). Further research must address a larger sample size and a refinement of the
experimental procedure in order to best understand differences between relaxed and occupied
conditions.
Introduction
As one of the most primitive defensive responses in the human body, the startle reflex
demonstrates the body’s quick, involuntary reaction to sudden external stimuli. These stimuli
may be visual or tactile, but are most commonly auditory (Dreissen et. al, 2011). In response to
the stimuli, a person may exhibit one or more motor responses such as an eye blink, a head
movement, an abdominal contraction, or a flexion of limbs (Cook et. al, 1991). In addition to
motor responses, the body’s cardiovascular and adrenal catecholamine systems will activate,
increasing the heart rate and dilating the bronchioles (Jansen et. al, 1995). The body’s startle
response is also characterized by increased blood pressure, as well as increased skin perspiration.
These responses result from the activation of the sympathetic division of the autonomic nervous
system (ANS). The other division of the ANS, the parasympathetic division, controls the body at
rest and is responsible for resolving sympathetic responses after danger has passed (Seeley et. al,
2004).
Previous studies have shown that the strength of the startle response can be suppressed if
a weaker startle stimulus or warning is presented prior to the actual startle stimulus (Braff et. al,
2001). This reduction in amplitude of the startle response reflects the ability of the nervous
system to temporarily adapt when given a warning. This has been recognized as pre-pulse
inhibition (PPI). Much like the startle reflex, a variety of visual, auditory, or tactile ‘prepulses’
can be applied to elicit adaptive physiological responses (Braff et. al, 2001). In addition, if a
‘prepulse’ is emotionally striking, it can elicit a greater reduction in the startle response (Filion
et. al, 1998). The duration and intensity of the startle reflex in response to a startle stimulus is a
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reflection of the individual’s personality and their emotional and physical state at the time of the
stimulus. Thus, the intensity of the startle reflex has been identified as a reflection of emotion,
particularly negative emotions such as fear and anger (Roy et. al, 2009). Since emotion arises
unconsciously, like the startle reflex, the individual’s autonomic responses offer reliable signs of
emotional reaction, such as anticipation, from the warning stimuli.
Previous research suggests that if subjects are introduced to a prepulse prior to the
excitatory stimulus, they were more prone to worry than those who did not receive the
‘prepulse’. A consequence of worrying about the impeding stimulus resulted in PPI and a
reduction in the physiological response to the stimulus. For example, in a study of
arachnophobic subjects, those instructed to imagine the spider before exposure to an actual
spider exhibited a smaller startle response, as represented by heart rate and skin conductance
responses (SCR), than those suddenly exposed to the actual spider (Castandeda & Sergerstrom,
2004). In addition, it has been shown that a subject sitting relaxed in a dark room had a smaller
cardiac response to the auditory stimuli when it was preceded by an auditory warning stimulus,
known as the prepulse, rather than by itself (Eder et. al, 2008).
In addition, researchers saw a reduction in a subject’s startle response when he or she was
focused on something other than the stimulus (Silverstein et. al, 1981). This is an example of an
adaptive physiological response the body creates depending on its environment. In a study by
Lang et. al, subjects engaged in an interesting activity exhibited a significantly smaller startle
reflex, as determined by their blink response, than those engaged in a dull activity (1990). This
adjustment of the startle response likely reflects the subject’s emotional anticipation at the time
of the stimuli, as the researchers believed interesting activity was more evocative of emotion.
The same research also concluded that subjects with anxiety often showed exaggerated startle
responses.
The purpose of this study is to determine whether a participant’s physiological response
to startle and warning stimuli are dependent on whether they are relaxed or occupied. In both
conditions, we expect the occupied group to exhibit a smaller physiological response than the
relaxed group. Since the subject is engaged in an activity they will allocate more of their
attentional resources to the primary task, leaving little attentional resources for the introduced
stimuli. In contrast, relaxed condition subjects will be able to allocate more attentional resources
to the stimuli since they are engaged in a dull activity (resting). We expect them to a have a
greater physiological response to both the warning and startle stimuli.
Materials & Methods
Sixteen participants (n = 16) were randomly recruited from Physiology 435: Lab 601 for
participation in this study. The participants included eight males and eight females. Participants
were divided into two groups, one of which involved an occupied condition (word search) and
the other of which involved a relaxed condition (no word search). Mean ages of all participants
were 22.19 years with a range of 20-45 years. The median age was 21 years. Each group
consisted of an 1:1 ratio of males to females.
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Before beginning the study, each participant was made aware of possible risks and asked
to sign a consent form as well as answer a brief questionnaire about their fearfulness (see
Supplemental Materials I-II). Fearfulness was rated on a scale of one to five, with five being the
most fearful. Each participant was informed the study would last approximately twenty minutes.
The participant was then taken to a quiet room and connected to the following equipment:
respiration transducer, electrocardiography (ECG), and galvanic skin response (GSR or SCR)
(see Supplemental Materials III). Experimental sessions took place individually for
approximately five minutes.
Upon attachment to all equipment, each participant was calibrated for respiration, ECG,
and GSR in the BIOPAC student lab program (see Supplemental Materials IV). All participants
were calibrated in the same way for each testing session. (Note: Comments were recorded
directly into BIOPAC Student Lab Program in order to track experimental progress.) The
participants next received verbal instructions as to what the task entailed. Participants were
informed of the commands issued in each part of the experiment. When the experimenter said,
“begin”, the participant would focus on a specific object for thirty seconds in a relaxed position
(see Figure 1). The data collected during this time period served as the negative control. Each
participant was his or her own baseline. The baseline provided the participant’s
parasympathetic, as well as sympathetic, activity while he or she was at rest.
Thirty seconds after beginning, the participant was told to either begin the relaxed
condition (RC) or occupied condition (OC) activity. He or she would continue this activity until
the experiment was finished. Thirty seconds after beginning the activity, each participant
received a warning stimulus from five feet away. The warning stimulus was four medium
volume, pure tone beeps produced from a smartphone application. Ten seconds after the
warning stimulus was given (total time: 70 sec), the participant was exposed to an auditory
startle stimulus. The auditory startle stimulus was a short, loud bang produced by a screwdriver
hitting a metal lid. It was introduced approximately one and a half feet behind the participant’s
head. At 100 seconds, participants were told the experiment was completed and that he or she
may leave. The participant was disconnected from all equipment and thanked for their
participation. Data was analyzed using Microsoft Excel.
Figure 1. Timeline: Occupied/Relaxed Condition.
On a separate day, each participant was again recruited to obtain his or her positive
control data (see Figure 2). The positive control data provided the participant’s parasympathetic,
as well as sympathetic, activity while he or she was vigorously riding a stationary bicycle. As
before, the participant was taken to the quiet room and connected to all measurements. Upon
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attachment, all measurements were calibrated. Verbal instructions were given to each
participant. To start, each participant remained at rest for 30 seconds while on the stationary
bicycle. After the 30 seconds, the participant began biking at a moderate speed for an additional
30 seconds. One minute into the experiment, the participants were told to bike for 40 seconds at
maximum speed. At the end of the 40 seconds, the positive control experiment was complete.
All equipment was disconnected and his or data was analyzed and compared to previously
obtained data.
Figure 2. Timeline: Positive Control.
Statistical analysis of the data was done using standard deviations and conducting a t-test
in order to determine a p-value. A p-value of less than 0.05 indicated significant differences
between the relaxed and occupied condition groups. During data analysis, three participants
(RC5, RC7, and OC3) were found to exhibit data points that differed greatly from the other
participants. In order to prevent skewing of the overall data, two study participants from the
relaxed condition group and one from the occupied condition group were removed. Exclusion of
these participants was based on whether or not their data clearly deviated from the calculated
averages.
Results
Emotion
Before beginning the study, participants were asked to complete a questionnaire (see
Supplemental Materials II) that asked them whether they consider themselves to be a fearful
person (fearfulness), whether loud noises tend to startle them (easily startled), and whether they
feel anxiety while completing mental puzzles (task anxiety). Group averages of subject
responses can be found in Table 1. Subjects in the relaxed condition had a 1.25 times higher
fearfulness and startle ratings than subjects in the occupied group. This could explain the higher
physiological responses observed in the relaxed condition.
Swerdlow NR, Monroe SM, Hartston HJ, Braff DL, Geyer MA, and Auerbach PP. (1993). Men
are more inhibited than women by weak prepulses. Biol Psychiatry 34, 253–261.
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Supplemental Materials
I. Consent Form
University of Wisconsin-Madison
Physiology 435 – Group 5
Research Participant Information and Consent Form
Title of the Study: Physiological Response to an Auditory Startle Stimulus under Relaxed and
Preoccupied Conditions.
Principle Investigators: Maddy Eckelaert, Michelle Cancel, Jai Patel, Zach Bennett, Miki Hirano,
Ashley Verhasselt
Description of the Research and Participant Involvement: I understand that I will be asked to either attempt to complete a word search as quickly as possible or
relax with my eyes closed during this experiment. While I am completing my given task, I will hear
a warning stimuli and I may or may not experience an auditory startle stimulus. I agree to have my
skin conductance, respiratory activity and heart rate monitored throughout the duration of the
experiment. The experiment should take approximately 20 minutes to complete.
Risks: There should be no significant health risks associated with this experiment but please do let the
experimenters know if you have a heart condition that may be provoked from being startled.
Benefits and Compensation: I understand that I do not stand to gain any favors by agreeing to take part in this experiment and that
I will not be penalized should I decide not to volunteer as a subject, or should I decide to withdraw
from participation. I also understand that there are no direct benefits to me by participating in this
experiment, but I may ask any of the experimenters of this study to participate in my study.
Confidentiality: Personal information will be kept confidential. Only group characteristics will be published.
Questions: I understand that I may ask questions about my rights as a subject, or register any complaint I might
have about the experiment with any of the researchers listed above.
Name (printed): _______________________________________________